Euclidea: A game where you complete/unlock basic geometric proofs (euclidea.xyz)

Loads fast, feels fast to use even on my old laptop. Cool stuff!

What would make it more fun: clicky sounds.

I am also thrilled by the quotes after each solution:

Education is what remains after one has forgotten everything he learned in school.

— Albert Einstein

Without geometry, life would be pointless.

— Joke